End mills are cutting tools used in tool holders and milling machines to remove material from metal, wood, and plastic workpieces. With cutting teeth along the outside diameter, end mills can create multi-dimensional shapes and profiles. Flutes remove chips from the cutting area and allow cooling fluids to enter. The number of flutes can range from two to eight. Fewer flutes offer the most efficient chip removal, but more flutes provide a smoother finish. The end mill’s helix angle is also a factor; a 30-degree helix angle is considered general purpose because it is the midpoint between “slow” (low-angle) and “fast” (high-angle) helix end mills.
Various styles of end mills are suitable for specific applications. Ball nose end mills are best for machining round bottom holes and complex contoured surfaces. Square nose end mills have square ends and are suitable for slotting, profiling, and roughing. Chamfer (also called drill-point) end mills have a point at the end and can be used for drilling, spotting, chamfering, and countersinking. Corner radius end mills have a square end with rounded corners on the cutting edges to reduce chipping. Corner rounding end mills take the sharp edges off external corners, while tapered end mills are suitable for die and mold operations. Double-ended end mills have cutting edges on both ends, allowing a new cutting surface to be substituted when the first shows wear, doubling the tool’s life compared to single-ended end mills.
Cutter material is an important consideration when selecting an end mill. Carbide can run at higher speeds than high-speed or cobalt steel, resisting wear and high cutting temperatures. High-speed steel is compatible with a variety of materials. Cobalt steel resists abrasion and high cutting temperatures, and has higher feed rates than high-speed steel.
Some end mills are uncoated, while others are coated with finishes to enhance performance. Most finishes extend the life of the end mill and allow higher cutting speeds and feed rates. For example, a titanium nitride (TiN) finish offers high-temperature resistance and increased hardness compared to uncoated end mills, while a titanium carbon nitride (TiCN) finish lubricates the end mill for high-temperature stability and offers better abrasion resistance than TiN coating.
An end mill’s end cut type is either center cutting or non-center cutting. Center-cutting end mills can create three-dimensional shapes and profiles, and make plunge cuts similar to a drill bit. Non-center-cutting end mills are suitable for peripheral milling and finishing, but cannot make plunge cuts.
The cutting diameter references the outside diameter of an end mill’s flutes. For tapered end mills, the cutting diameter is measured at the tip of the tool, not the shank.
There are three cut types for end mills. Finishing end mills provide a smoother surface finish than general purpose or roughing end mills. General purpose end mills can be used for a range of applications, and provide a smoother finish than roughers. Roughing end mills remove more material in less time than general purpose end mills, with minimal vibration (chatter). They create a rough finish that can be smoothed by a second finishing cut.